Formic acid directly assisted solid-state synthesis of metallic catalysts without further reduction: As-prepared Cu/ZnO catalysts for low-temperature methanol synthesis

Metallic catalysts (Cu/ZnO) and pure metals (Co, Ni, and Ag) without any impurities are directly prepared by a novel formic acid-assisted solid-state method without further reduction. During the decomposition of metal–formic acid precursors at 523 K under argon, H2 and CO are liberated and act in situ as reducing agents to obtain pure metals and metallic catalysts (Cargon). X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive spectroscopy, and temperature-programmed reduction analysis reveal that the as-prepared catalyst Cargon without further reduction is converted into metallic Cu0 and ZnO species. TPR analysis results, Fourier transform infrared analysis, and the thermal decomposition behavior in air illustrate that no amorphous carbon or carbonic residues are left in Cargon when formic acid is used as the chelating agent and reductant, because formic acid is the simplest organic acid. The as-prepared Cu/ZnO catalyst is tested for low-temperature methanol synthesis at 443 K from syngas containing CO2 and using ethanol as a solvent and catalyst; it exhibits much higher activity and methanol selectivity than catalysts prepared by conventional solid-state methods.